package com.jwt.server.util;


import java.net.InetAddress;
import java.net.UnknownHostException;

import org.apache.commons.lang3.time.DateFormatUtils;

import lombok.extern.slf4j.Slf4j;

/**
 * 与snowflake算法区别,返回字符串id,占用更多字节,但直观从id中看出生成时间
 *
 */
@Slf4j
public enum IdGenerator {
	/**
	 * 每个要生成的序号类型对应一个序号
	 */
	USER_TRANSID("1");

    private long workerId;   //用ip地址最后几个字节标示
    private long datacenterId = 0L; //可配置在properties中,启动时加载,此处默认先写成0
    private long sequence = 0L;
    private final long twepoch = 1516175710371L;
    private final long workerIdBits = 1L;
    private final long datacenterIdBits = 2L;
    private final long sequenceBits = 3L;
    private final long workerIdShift = sequenceBits;
    private final long datacenterIdShift = sequenceBits + workerIdBits;
    private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    private long sequenceMask = -1L ^ (-1L << sequenceBits); //4095
    private long lastTimestamp = -1L;

    private String index;
    
    IdGenerator(String ind) {
        this.index = ind;
        workerId = 0x000000FF & getLastIP();
    }

    public synchronized String nextId() {
        long timestamp = timeGen(); //获取当前毫秒数
        //如果服务器时间有问题(时钟后退) 报错。
        if (timestamp < lastTimestamp) {
            throw new RuntimeException(String.format(
                    "Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }
        //如果上次生成时间和当前时间相同,在同一毫秒内
        if (lastTimestamp == timestamp) {
            //sequence自增，因为sequence只有12bit，所以和sequenceMask相与一下，去掉高位
            sequence = (sequence + 1) & sequenceMask;
            //判断是否溢出,也就是每毫秒内超过4095，当为4096时，与sequenceMask相与，sequence就等于0
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp); //自旋等待到下一毫秒
            }
        } else {
            sequence = 0L; //如果和上次生成时间不同,重置sequence，就是下一毫秒开始，sequence计数重新从0开始累加
        }
        lastTimestamp = timestamp;

        long suffix =  ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;
        
        String datePrefix = DateFormatUtils.format(timeGen(), "yyyyMMddHHmmss");
        return datePrefix +index + suffix;
    }
    

    private long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }

    private long timeGen() {
        return System.currentTimeMillis();
    }

    private byte getLastIP(){
        byte lastip = 0;
        try{
            InetAddress ip = InetAddress.getLocalHost();
            byte[] ipByte = ip.getAddress();
            lastip = ipByte[ipByte.length - 1];
        } catch (UnknownHostException e) {
        	log.error("UnknownHostException error：{}", e.getMessage());
        }
        return lastip;
    }
    
    public static void main(String[] args) {
		IdGenerator id = IdGenerator.USER_TRANSID;
		for (int i = 0; i < 1000; i++) {
			String serialNo = id.nextId();
			System.out.println(serialNo + "===" + serialNo.length());
		}
	}
}